70 



FLUORESCENCE OF THE URANYL SALTS. 



(2) That lack of resolution in any region may give the appearance of 

 a single band with intermediate crest in place of the doublet. 



(3) That the position of crests of the unresolved doublets at +20 

 will not necessarily coincide exactly with that of either component. 



Bearing these points in mind, it will be seen that were resolution 

 complete all the observed bands of the spectrum at 185 would 

 probably fall into the system proposed above. 



We may imagine that the difference between the resolution of the 

 bands C and D, for example, as seen in figure 54, is produced by changes 



in the unresolved doublets at 

 +20 when the temperature 

 is reduced to 185, of the 

 kind indicated in figure 59. 

 The doublet CC" forms a 

 single band with crest nearly 

 coincident with C at +20, 

 and this owing to the sub- 

 sidence of C and growth of 

 C' takes the resolved form 

 shown at 185. In the case 

 of D, however, the unresolved 



-20 



FIG. 58. 



-185" 



Fia. 59. 



-20 -185 



band has an intermediate crest at D, but is really composed of over- 

 lapping components D' and D" which are separately visible at 185. 



The wave-lengths and frequencies of the bands in the resolved 

 spectra of the four double chlorides, as observed when excited at the 

 temperature of liquid air, are given in table 31 at the end of the chapter. 

 The nomenclature used in this and subsequent tables is chosen to 

 indicate as far as possible the relation of the bands at 185 to those 

 at +20. Thus BI, B 2 , etc., denote components of B, etc., which have 

 been rendered visible by the resolution effected by cooling. 



The explanation offered above to account for the relation between 

 the spectra at +20 and at 185, and which was illustrated in the 

 case of the ammonium uranyl chloride (see fig. 58), was confirmed by 

 observations upon the spectrum of that salt at intermediate tempera- 

 tures. It was thus possible to watch the gradual appearance of the 



